setup.sh: fix /etc/sudoers.d permissions

gitlab runs ci jobs with umask 0000 to prevent issues with file
permissions. sudo refuses to look at configuration files in
/etc/sudoers.d if it is world-writable.

Fix these permissions so that sudo still works.
3 jobs for fix-sudoersd-permisions in 1 minute and 2 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed build-s390x #630
docker-alpine s390x

00:00:52

passed build-x86 #632
docker-alpine x86

00:01:02

passed build-x86_64 #631
docker-alpine x86_64

00:00:55